Previous work from this laboratory (Hardy, Hirshaut, et al, 1970, 1973) provided an immunologic assay that permitted the horizontal transmission of feline leukemia virus and its associated malignancy, feline lymphosarcoma, to be demonstrated. Since 1970 we have also delineated 3 antigenic markers of human sarcoma, S1, S2, and S3. The prevalence of antibody to S2 and S3 is higher in immediate family members of patients than in the general population. An increased prevalence of S1 antibody has also been found in family members about age 40. The relatively high prevalence of antibody to sarcoma markers in individuals who are in close contact with patients suggests that as in cats the etiologic agent of such tumors may be horizontally transmissible. It is proposed to collect prospectively, sera from patients, age-sex-matched controls and immediate and distant family members. The probands (index cases), their relatives and controls will be interviewed, complete an epidemiologic questionnaire, and contribute serum samples every 3 months for 2 years. Sera obtained, particularly from immediate patient contacts, will be used to search for new sarcoma markers. Immune assays include immunofluorescence, complement fixation and microcytotoxicity. As sera are accumulated they will be tested for antibody to known and newly identified sarcoma atigens. Comparisons will be made of antibody prevalence and seroconversion observed among those in immediate contact with the patient and those at a distance. The 3 goals of this proposal (a) prospective collection of close and distant family sera from patients with sarcoma, (b) use of family sera for detection of sarcoma antigens, and (c) search for seroepidemiologic evidence of transissibility of human sarcoma, are each independently of importance and likely to eventually provide new insight into the etiology of human neoplasms.